Keshab Raj Pande, Suchit Shrestha, Mathias Becker:
Managing Soil N-dynamics in Rice-wheat Cropping Systems Along an Altitude Gradient in Nepal

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KESHAB RAJ PANDE1, SUCHIT SHRESTHA2, MATHIAS BECKER1
1University of Bonn, Plant Nutrition in the Tropics and Subtropics, Germany
2Nepal Agricultural Research Council, Rars Lumle, Nepal

The rice-wheat annual double cropping system occupies some 0.5 million ha in Nepal along a gradient between the tropical lowlands of the Terai and the subtropical mid-hills of the Himalayas. Mineral N fertiliser use in the predominant smallholder agriculture is low and crops rely largely on native soil N for their nutrition. Alternating soil drying and wetting cycles stimulate N losses, particularly during the 1-3 months dry-to-wet season transition period (DWT) after the harvest of wheat and before the transplanting of rice. Soil N uptake by nitrate-catch crops grown during DWT, sole or in combination with wheat straw application (temporary microbial N immobilisation), has been shown to reduce N losses and to significantly increase rice yield with residual yield effects on the subsequent crop of wheat. However, the choice of DWT crops needs to be matched to farmers' preferences and to the different climatic conditions prevailing in the agroecological zones of Nepal where rice and wheat are grown. The feasibility and the adoption potential of options vary along the altitude gradient (length of DWT, seasonal temperate variations) and by farmer's resources and production objectives (food preferences, alternative uses of straw, market access). Field experiments were conducted on farmers' fields at three sites along an altitude gradient in Nepal between 2003 and 2004. The sites included the temperate highlands at 2000m altitude, the subtropical foothills of the Himalayas at 600m altitude and the (sub)-tropical lowlands of the Terai. Technical options comprised a wide range of ``nitrate catch crops'', several nitrogen"=fixing green manures and various rates of wheat straw, applied sole or in combination with the transition season crops. Key findings on soil nitrogen dynamics and performance parameters of rice and wheat will be presented. Computer"=based decision tools are being developed to provide a quantitative base for improved cropping calendar planning and the identification of target areas for site"=specifically-adapted crop options.



Keywords: Mucuna, Oryza sativa, Triticum aestivum, Vigna


Footnotes

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Contact Address: Mathias Becker, University of Bonn, Plant Nutrition in the Tropics and SubtropicsKarlrobert Kreiten Straße 13, 53115 Bonn, Germany, e-mail: mathias.becker@uni-bonn.de
Andreas Deininger, September 2004